In mining, especially for coal deposits or the like, normally one or more access tunnels or entries are cut into the seam or deposit to be mined. In one commonly used method, called the longwall method, the product is cut with a shearer or plow from a wall of the mine and removed by a conveyor or other means until the plow has been moved the desired distance into the deposit. As the cavity from where the mined product has been removed becomes large, the roof begins to crumble and fall into the mine. Thus, each time the plow removes portions of the wall, the roof supports and the conveyor or other removal means are moved towards the new wall or face, and the roof in the direction away from the plow progression crumbles into the mine. See, e.g., the description of longwall mining by Janssen in U.S. Pat. No. 3,892,442.
A number of methods have been used to prevent the roof of subterranean formations from falling. Typically, either timbers frames or rock-bolts are used to create a supporting structure that prevents the roof of the mine in direct contact with the supporting structure from falling. In timber framing operations, timbers are used to build a frame around the periphery of the mine such that a supporting structure is formed. In rock-bolting operations, a hole is drilled into a subterranean formation wherein a self-setting composition is used to secure an anchor bolt. Typically, such self-setting compositions are provided in a cartridge which comprises a resin and a catalyst. For example, Plaisted in U.S. Pat. No. 4,260,699, discloses a polyester adhesive system and a method of using the system in a cartridge containing a resin and a catalyst.
However, the above methods for supporting subterranean formations are not always acceptable or easily performed. Thus, stabilizing compositions, which are pumped into cracks and crevices in the underground formation, are often utilized to stabilize the formation. Various compositions have been used to stabilize and strengthen the roof and walls of the formation. Many stabilizing systems have been proposed ranging from relatively simple cement based systems to complex, relatively costly gel-based systems containing water-soluble acrylamide copolymers and various phenol formaldehyde resins.
Typically, however, most stabilizing compositions have not met with much commercial success as it is preferred that they contain relatively inexpensive components which are in plentiful supply; facilitate injection into the cracks and crevices in the formation; stabilize the load-bearing walls or other formation into a stable, rigid, water-resistant structure of substantial strength; be resistant to shrinkage; cure in a relatively short, but controllable, amount of time; and be relatively inert and non-toxic to avoid danger of injury to operating personnel and contamination of the area surrounding the formation.
Polyester resin compositions, as well as many other synthetic resin systems, has been proposed for use in grouting subterranean formations. For example, Brown et al., in U.S. Pat. No. 3,091,935, and Lundberg et al., in U.S. Pat. No. 3,091,936, have proposed the use of polyester grout compositions. However, the polyester systems described therein suffer from the disadvantage of being susceptible to shrinkage that may result in a catastrophic failure of the underground formation.
Consequently, polyurethane-based grouting systems are typically used to increase the load-bearing capacity of walls in underground mining when the composition is pumped into cracks and crevices within the mine. The polyurethane-based systems provide the desired strength and stability required of stabilizing compositions. For example, Muller et al., in U.S. Pat. No. 4,965,297, disclose a process for strengthening geological formations by the introduction of a composition which reacts to form polyurethane plastics in the formations. Typically, such reaction mixtures are based on a polyisocyanate component, a polyol component and various auxiliary agents and additives.
Polyurethane based systems, however, present significant health and safety hazards associated with the use of large amounts of isocyanates in enclosed and underground spaces. As will be appreciated by those skilled in the art, hazards such as emission of poisonous or noxious fumes, dust and the like, especially in mining operations, are particularly troublesome. Such fumes, dust and the like must be controlled or removed from the mine to prevent injury to mine workers. Ventilation techniques used to control such fumes typically employ systems which are expensive to maintain and operate, and which require elaborate planning to provide proper air flow paths.
In summary, state-of-the-art compositions and processes are susceptible to one or more disadvantages including slow gelling or curing rates; difficulty in injection into earth formations; shrinkage; sensitivity to the environment during injection and curing; and hazardous emissions. Thus, there remains a long-felt need to provide improved stabilizing compositions and methods of stabilizing subterranean formations.